Visible light communication is a communication technology which uses the variation of visible light (color, intensity, or position) to transmit information. Such communication technology for transmitting information is based on high-frequency blinking visible lights. In particular, information to be transmitted is firstly compiled into a digital signal; this digital signal is then applied to modulate the driving current or driving voltage of the light source by pulse width modulation (PWM), so that the light source blinks in high frequencies. This high-frequency blinking signal can be detected by a photosensitive device, for example, an image sensor such as a photodiode, and can be restored back into the transmitted information. The main advantages of this visible light communication technology are high confidentiality, no occupancy of wireless channel resources, low cost, and easy integration with LED.
One of the existing visible light communication technologies is based on the “rolling shutter” mechanism of image sensors. In such sensors, different parts of the sensor, each row or each column, are exposed at different times. Based on this feature, when taking pictures of a light source with rapidly changing brightness, the image sensor with a rolling shutter can deliver an image which contains bright and dark stripes. By measuring the width, the number, or the gray scale of the stripes, the transmitted information can be restored. However, this method has the following drawbacks: the width of the stripes can be affected by local over-exposure of the image sensor, for instance, stripes may become narrower within the over-exposed area; coding only based on the changing numbers of the stripe will lead to a low communication rate; and different background lighting conditions may induce uncertainties for measuring the gray scale.